Author Topic: Starship Expendable Upper Stage?  (Read 44694 times)

Online TheRadicalModerate

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Re: Expendable Upper Stage?!?
« Reply #60 on: 02/02/2023 09:29 pm »
The "traditional" alternative would be to send ISS modules that will fit into the SS cargo bay and assemble them in space. Nominal SS cargo payload volume is listed at 9 meter diameter by 18 meter "height", but I suspect the actual payload must be a bit smaller: call it 8 meters in diameter. One module would be at least 5 times the volume of an existing ISS module.

From the Starship User Guide (which is probably stale, but I doubt they've changed the payload bay static envelope), see attached.  Note also that there's an "extended" configuration with a 22m height, which I suspect is an expendable Starship without header tanks, but could be a different outer mould line.

Online TheRadicalModerate

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Re: Expendable Upper Stage?!?
« Reply #61 on: 02/02/2023 09:33 pm »
Let’s say the heat shield issue can never be reliably solved for rapid, cheap upper stage reuse.

In that case, Starship can still be a greatly improved evolution of F9. My interest is, how much cheaper can a partially reusable Starship be than a partially reusable F9, on a kg to LEO basis?

That would largely depend on the cost of expending the upper stage. So I then ponder on how the upper stage can be easily redesigned to be as cheap as possible? Does it simply become an upsized F9 upper stage? In that case you can have a flared out, detachable and recoverable fairing (upsized from F9’s fairing), allowing for payloads significantly exceeding 9m in diameter.

In my view, even if such a partially reusable configuration is the best Starship ever achieves, it can still probably get to around a $30M launch cost, for 150t to LEO.

That’s ~$200/kg, which is  ~7 times cheaper than F9’s ~$1500/kg cost to LEO.

That in itself revolutionises the industry.

Have been thinking along the same lines. The partially reusable version can sustain NASA's HLS, Starlink, and many other nice things, even up to a NASA-led humans to Mars mission. This would actually be a huge success, and ten years before China aims to field a comparable system.

There's nothing particularly expensive about the Starship stage, other than the engines.  If you have lighter payloads, you can de-engine the silly thing, rip the elonerons and TPS off, and it's not much more than a bunch of stainless steel with some avionics and (fewer) engines.  You don't need new stages; you just need a dumber Starship.

Online TheRadicalModerate

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Re: Expendable Upper Stage?!?
« Reply #62 on: 02/03/2023 03:37 am »
*snip*
¹Did we get an answer for whether 250t to LEO is with only an expendable Starship, or does it require expending the SuperHeavy as well?
Probably with expendable Starship only. Musk does specify in the Tweet "expendable upper stage."
...

If only the upper stage is expended, then isn't there a 1:1 correspondence between the additional payload to orbit and the landing propellant, header tanks, heat shields, and body flaps which are not needed for an expendable mission?

Where is the 100t found (to increase payload from 150t reusable to 250t expendable) if the dry Starship only weighs ... what? ~ 85 - 100t?  How much landing propellant are we talking about?

It's very close to 1:1, but you've left off a biggie:  You can jettison the whole nose fairing pretty early in the ascent.  I suspect that's good for close to 50t-70t extra payload right there.  I've been assuming that all the elonerons, TPS, header tanks, and residuals are good for at least 25t, so now we're getting pretty close.

This of course assumes that the vanilla-flavored Starship can actually get 150t to LEO, which isn't a done deal yet.  And I'd also guess that the baseline for the 250t claim assumes the existence of "Raptor Full-Thrust", as well, which reputedly takes the vanilla mass to LEO to almost 200t.

Offline M.E.T.

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Re: Expendable Upper Stage?!?
« Reply #63 on: 02/03/2023 03:57 am »
*snip*
¹Did we get an answer for whether 250t to LEO is with only an expendable Starship, or does it require expending the SuperHeavy as well?
Probably with expendable Starship only. Musk does specify in the Tweet "expendable upper stage."
...

If only the upper stage is expended, then isn't there a 1:1 correspondence between the additional payload to orbit and the landing propellant, header tanks, heat shields, and body flaps which are not needed for an expendable mission?

Where is the 100t found (to increase payload from 150t reusable to 250t expendable) if the dry Starship only weighs ... what? ~ 85 - 100t?  How much landing propellant are we talking about?

It's very close to 1:1, but you've left off a biggie:  You can jettison the whole nose fairing pretty early in the ascent.  I suspect that's good for close to 50t-70t extra payload right there.  I've been assuming that all the elonerons, TPS, header tanks, and residuals are good for at least 25t, so now we're getting pretty close.

This of course assumes that the vanilla-flavored Starship can actually get 150t to LEO, which isn't a done deal yet.  And I'd also guess that the baseline for the 250t claim assumes the existence of "Raptor Full-Thrust", as well, which reputedly takes the vanilla mass to LEO to almost 200t.

This is the important point that the “400t expendable” proponents are missing.

Starship in its current format is likely not down to 85t dry mass, and Raptor in its current form is likely gonna operate well below Elon’s optimised, aspirational levels.

So I would not be surprised if reusable Starship is initially just a 75t to LEO vehicle.

With optimisation gradually pushing it towards the 100t mark. With 150t the distant stretch goal, assuming a lot of aspirational progress.

So 250t is likely the realistic fully expendable  capacity, if I had to put money on it - for the 2020’s at least.
« Last Edit: 02/03/2023 03:58 am by M.E.T. »

Offline Valerij

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Re: Expendable Upper Stage?!?
« Reply #64 on: 02/03/2023 10:42 am »
The "250 tonne expendable" refers to a payload delivered by an expendable SS atop an expendable booster.

I, like all of us, cannot confirm my words with a calculation due to the lack of accurate initial data. But I got the impression that 250 tonns in orbit is a expendable Starship on a reusable booster. I'll try to explain why I have such an opinion.
     
Yes, I agree, a expendable Starship should not have thermal protection tiles, aerodynamic planes, part of the fuel plant, intended for return, but this is a lot less than a hundred tonns in total.
   
As I understand it, a reusable Starship must have about 40 tonns of fuel in its tanks to return to Earth. Unlike it, the expendable Starship can use these forty tonns of fuel to enter orbit, and therefore may have an additional supply of fuel in excess of these forty. In my opinion, due to an increase in the available fuel supply and a decrease in the mass of the Starship itself, its maximum carrying capacity is growing to 250 tonns.
   
That is, the starting mass of a expendable Starship may be more due to for more fuel and more payload.
   

Offline Valerij

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Re: Expendable Upper Stage?!?
« Reply #65 on: 02/03/2023 10:55 am »
   
The "traditional" alternative would be to send ISS modules that will fit into the SS cargo bay and assemble them in space. Nominal SS cargo payload volume is listed at 9 meter diameter by 18 meter "height", but I suspect the actual payload must be a bit smaller: call it 8 meters in diameter. One module would be at least 5 times the volume of an existing ISS module.
   
Of course, this is pure speculation, but I assume that after some time we will see a custom Starship with an "over-caliber" payload bay. That is, on the usual section of engines and tanks with a diameter of 9 meters there will be a payload compartment, or fairing, with a diameter of 12-15 meters. I think, this is a very interesting configuration for space stations...

Offline eriblo

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Re: Expendable Upper Stage?!?
« Reply #66 on: 02/03/2023 11:11 am »
The "250 tonne expendable" refers to a payload delivered by an expendable SS atop an expendable booster.

I, like all of us, cannot confirm my words with a calculation due to the lack of accurate initial data. But I got the impression that 250 tonns in orbit is a expendable Starship on a reusable booster. I'll try to explain why I have such an opinion.
     
Yes, I agree, a expendable Starship should not have thermal protection tiles, aerodynamic planes, part of the fuel plant, intended for return, but this is a lot less than a hundred tonns in total.
   
As I understand it, a reusable Starship must have about 40 tonns of fuel in its tanks to return to Earth. Unlike it, the expendable Starship can use these forty tonns of fuel to enter orbit, and therefore may have an additional supply of fuel in excess of these forty. In my opinion, due to an increase in the available fuel supply and a decrease in the mass of the Starship itself, its maximum carrying capacity is growing to 250 tonns.
   
That is, the starting mass of a expendable Starship may be more due to for more fuel and more payload.
   
Unless they spend a lot more time hovering than they did during the test flights deorbit + landing is < 400 m/s which is ~30 t of propellant even with full payload. Quoting from another thread:
 
Expendable payload has been estimated as ~2x reusable which gives HLS + 2 tankers with quite a bit of margin for boiloff and residuals.
There's no way it takes an extra 100t of propellant to reuse a Starship.

1.2x I'd believe, but not 2x
It's not just the propellant. If SS is designed to be expendable it does not have TPS or Elonerons.
Do the math, you still don't get 2x
Have you done the math? flightclub.io has a Starship profile (120 t payload, 119 t + 250 t dry mass, 1200 t + 2970 t of propellant) that gets to a ~200 km orbit with 12 t of residuals/landing propellant.

Expending the booster gets ~50 t of residuals. Loading the booster fully with 3400 t gets ~87 t of residuals.

If we say that TPS + flaps + actuators + smaller batteries + payload bay is a conservative 23 t that would mean a stripped down tanker would deliver 230 t of propellant even before extending it and launching it heavy.

Online TheRadicalModerate

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Re: Starship Expendable Upper Stage?
« Reply #67 on: 02/03/2023 07:19 pm »
FWIW, here's a Silverbird calculation with:

SuperHeavy, with somewhat improved thrust (255.1tf):
dry=200t, prop=3400t, Thrust=33 x 2500kN = 82,500kN, launch Isp=333s

Expendable Starship with 50t jettisonable fairing, 9 engines, and avg 265.3tf thrust:
dry=95t, prop=1200t, Thrust=9 x 2600kN avg = 23,400kN, avg vac Isp=370s

Launched from Canaveral into 200km x 200km x 28.5º.

Midpoint is 213t payload to LEO.  95% CI is 164.2t - 271.5t

This is de facto a fully expendable (both SH and SS) calculation, with (assumed) nominal residuals.  It is of course possible that Silverbird's set of approximations doesn't work very well with something this big, but it implies that 250t might be... aspirational?

Offline InterestedEngineer

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Re: Starship Expendable Upper Stage?
« Reply #68 on: 02/03/2023 07:31 pm »
FWIW, here's a Silverbird calculation with:

SuperHeavy, with somewhat improved thrust (255.1tf):
dry=200t, prop=3400t, Thrust=33 x 2500kN = 82,500kN, launch Isp=333s

Expendable Starship with 50t jettisonable fairing, 9 engines, and avg 265.3tf thrust:
dry=95t, prop=1200t, Thrust=9 x 2600kN avg = 23,400kN, avg vac Isp=370s

Launched from Canaveral into 200km x 200km x 28.5º.

Midpoint is 213t payload to LEO.  95% CI is 164.2t - 271.5t

This is de facto a fully expendable (both SH and SS) calculation, with (assumed) nominal residuals.  It is of course possible that Silverbird's set of approximations doesn't work very well with something this big, but it implies that 250t might be... aspirational?

50t seems like very heavy for a faring, but dropping it in half only helps about 10t.

when I set the fairing to 10t and the dry mass of SS to 70t I get 250t.

(I also set Isp for first stage to 345.  It's only 333 the first few kilometers, vacuum Isp is 355).

Second stage is 365, which is what you get with all vacuum engines 100% and the regular at 50% thrust.
« Last Edit: 02/03/2023 07:35 pm by InterestedEngineer »

Online TheRadicalModerate

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Re: Starship Expendable Upper Stage?
« Reply #69 on: 02/03/2023 08:08 pm »
FWIW, here's a Silverbird calculation with:

SuperHeavy, with somewhat improved thrust (255.1tf):
dry=200t, prop=3400t, Thrust=33 x 2500kN = 82,500kN, launch Isp=333s

Expendable Starship with 50t jettisonable fairing, 9 engines, and avg 265.3tf thrust:
dry=95t, prop=1200t, Thrust=9 x 2600kN avg = 23,400kN, avg vac Isp=370s

Launched from Canaveral into 200km x 200km x 28.5º.

Midpoint is 213t payload to LEO.  95% CI is 164.2t - 271.5t

This is de facto a fully expendable (both SH and SS) calculation, with (assumed) nominal residuals.  It is of course possible that Silverbird's set of approximations doesn't work very well with something this big, but it implies that 250t might be... aspirational?

50t seems like very heavy for a faring, but dropping it in half only helps about 10t.

when I set the fairing to 10t and the dry mass of SS to 70t I get 250t.

(I also set Isp for first stage to 345.  It's only 333 the first few kilometers, vacuum Isp is 355).

Second stage is 365, which is what you get with all vacuum engines 100% and the regular at 50% thrust.

I was assuming that the dry mass included the fairing, which was then subtracted after the jettison time.  The fairing would be the entire nose of the vehicle.  There will be no header tanks, but the nose is really designed to maximize payload bay volume, rather than minimizing dynamic pressure loads.  I guess they could make a radically different fairing and slap it onto the propulsion section, but that seems like quite a bit more work.

I was also assuming that you plugged in SL Isp for the first stage, but it appears that's wrong and it should be vac Isp.  That takes the midpoint up to 235.8t.

Offline InterestedEngineer

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Re: Starship Expendable Upper Stage?
« Reply #70 on: 02/03/2023 08:18 pm »
FWIW, here's a Silverbird calculation with:

SuperHeavy, with somewhat improved thrust (255.1tf):
dry=200t, prop=3400t, Thrust=33 x 2500kN = 82,500kN, launch Isp=333s

Expendable Starship with 50t jettisonable fairing, 9 engines, and avg 265.3tf thrust:
dry=95t, prop=1200t, Thrust=9 x 2600kN avg = 23,400kN, avg vac Isp=370s

Launched from Canaveral into 200km x 200km x 28.5º.

Midpoint is 213t payload to LEO.  95% CI is 164.2t - 271.5t

This is de facto a fully expendable (both SH and SS) calculation, with (assumed) nominal residuals.  It is of course possible that Silverbird's set of approximations doesn't work very well with something this big, but it implies that 250t might be... aspirational?

50t seems like very heavy for a faring, but dropping it in half only helps about 10t.

when I set the fairing to 10t and the dry mass of SS to 70t I get 250t.

(I also set Isp for first stage to 345.  It's only 333 the first few kilometers, vacuum Isp is 355).

Second stage is 365, which is what you get with all vacuum engines 100% and the regular at 50% thrust.

I was assuming that the dry mass included the fairing, which was then subtracted after the jettison time.  The fairing would be the entire nose of the vehicle.  There will be no header tanks, but the nose is really designed to maximize payload bay volume, rather than minimizing dynamic pressure loads.  I guess they could make a radically different fairing and slap it onto the propulsion section, but that seems like quite a bit more work.

I was also assuming that you plugged in SL Isp for the first stage, but it appears that's wrong and it should be vac Isp.  That takes the midpoint up to 235.8t.

When I use what i think are reasonable numbers the reusable config easily gets 150t


Offline MickQ

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Re: Starship Expendable Upper Stage?
« Reply #71 on: 02/03/2023 10:14 pm »
Would there be any noticeable gain / loss in deleting the sea level engines and just running
the RVAC’s ??
« Last Edit: 02/03/2023 10:16 pm by MickQ »

Offline Steve D

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Re: Starship Expendable Upper Stage?
« Reply #72 on: 02/03/2023 10:16 pm »
If you want an expendable or non returnable starship could you lighten it by building it out nof aluminum?

Offline MickQ

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Re: Starship Expendable Upper Stage?
« Reply #73 on: 02/03/2023 10:38 pm »
One payload that comes to mind is a bigger and much more capable optical space telescope.
Imagine a 7+ metre monolithic mirror 🤔

Online TheRadicalModerate

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Re: Starship Expendable Upper Stage?
« Reply #74 on: 02/03/2023 11:33 pm »
Would there be any noticeable gain / loss in deleting the sea level engines and just running
the RVAC’s ??

With only 3 RVacs and no gimbaling, doing control just by throttling is dicey.  And things get really dicey if one of the RVacs fails.

On the other hand, if they really go to 6 RVacs + 3 RSLs, then deleting the 3 RSLs leaves a pretty robust system.  You might get into T/W trouble with extremely heavy payloads, though.  There's still some gravity drag to be incurred after SuperHeavy is gone.

Offline DanClemmensen

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Re: Starship Expendable Upper Stage?
« Reply #75 on: 02/03/2023 11:58 pm »
One payload that comes to mind is a bigger and much more capable optical space telescope.
Imagine a 7+ metre monolithic mirror 🤔
It appears That Subaru is the largest monolithic mirror on Earth. The mirror is 8.2 m diameter with a mass of 22.8 tonnes. Should easily fit in a standard reusable SS.  But why?  A bigger segmented mirror is probably a better choice.
   https://subarutelescope.org/en/about/

Offline livingjw

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Re: Starship Expendable Upper Stage?
« Reply #76 on: 02/04/2023 02:18 am »
If you want an expendable or non returnable starship could you lighten it by building it out nof aluminum?

- No, the strength to weight of 300 series SS used in Starship is higher than most high strength aluminum alloys.

John
« Last Edit: 02/04/2023 02:26 am by livingjw »

Offline Zed_Noir

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Re: Starship Expendable Upper Stage?
« Reply #77 on: 02/04/2023 03:55 am »
One payload that comes to mind is a bigger and much more capable optical space telescope.
Imagine a 7+ metre monolithic mirror 🤔
It appears That Subaru is the largest monolithic mirror on Earth. The mirror is 8.2 m diameter with a mass of 22.8 tonnes. Should easily fit in a standard reusable SS.  But why?  A bigger segmented mirror is probably a better choice.
   https://subarutelescope.org/en/about/
Not really. IIRC the internal diameter of the Starship is about 8 meters. Something like the Subaru monolithic mirror needs to be mounted in a telescope structure that is likely to have a bigger diameter than the 9 meter external diameter of the Starship .

Of course a 15-ish meter diameter mirror could fitted in a large asymmetric payload fairing shaped like an arrowhead on top of an expendable Starship variant.

Offline su27k

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Re: Starship Expendable Upper Stage?
« Reply #78 on: 02/04/2023 04:11 am »
One payload that comes to mind is a bigger and much more capable optical space telescope.
Imagine a 7+ metre monolithic mirror 🤔
It appears That Subaru is the largest monolithic mirror on Earth. The mirror is 8.2 m diameter with a mass of 22.8 tonnes. Should easily fit in a standard reusable SS.  But why?  A bigger segmented mirror is probably a better choice.
   https://subarutelescope.org/en/about/
Not really. IIRC the internal diameter of the Starship is about 8 meters. Something like the Subaru monolithic mirror needs to be mounted in a telescope structure that is likely to have a bigger diameter than the 9 meter external diameter of the Starship .

That's why it may be a job for expendable Starship: Use the ship structure itself as telescope structure and leave the ship in space (since it _is_ the telescope). Pretty sure Elon mentioned something like this before.

Offline Zed_Noir

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Re: Starship Expendable Upper Stage?
« Reply #79 on: 02/04/2023 05:09 am »
One payload that comes to mind is a bigger and much more capable optical space telescope.
Imagine a 7+ metre monolithic mirror 🤔
It appears That Subaru is the largest monolithic mirror on Earth. The mirror is 8.2 m diameter with a mass of 22.8 tonnes. Should easily fit in a standard reusable SS.  But why?  A bigger segmented mirror is probably a better choice.
   https://subarutelescope.org/en/about/
Not really. IIRC the internal diameter of the Starship is about 8 meters. Something like the Subaru monolithic mirror needs to be mounted in a telescope structure that is likely to have a bigger diameter than the 9 meter external diameter of the Starship .

That's why it may be a job for expendable Starship: Use the ship structure itself as telescope structure and leave the ship in space (since it _is_ the telescope). Pretty sure Elon mentioned something like this before.

Have doubts that the Starship structure is stable enough for use as a telescope structure without a lot of modifications. Might just be cheaper to not use the Starship as a telescope and build a new space telescope instead.
« Last Edit: 02/04/2023 06:56 am by Zed_Noir »

 

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